When some or all of system functions have faults or failures, a fault-tolerant system performs a failover operation to failover the faulty system functions. The failover operation is usually used in a stability-critical system and a mission-critical system whose faults or failures may result in injuries to people or property damage. The failover operation is widely used in various fields such as atomic power generation, energy generation, national defense, aviation, space, vehicle, railroad, shipbuilding, plant industry, finance, and medical treatment.
The fault-tolerant system may use, for example, a redundancy or replication method using additional hardware devices. The redundancy or replication method is mainly applied to a large server system or a network system in which continuance of services needs to be ensured. Also, the redundancy or replication method is applied to some hardware devices forming a power supplier, a central processing unit (CPU), a memory, a hard drive, etc. in order to prevent a single point of failure.
In detail, according to the redundancy or replication method, although hardware, which is critical to provide the services, or a single element stops operating or has a fault, an object which is the same as the hardware or the single element starts operating, and thus, the services may continue to be provided.
However, according to technology of the related art, some portions or an entire portion of hardware forming a system, for example, a computing server, a network switch, components, etc. are replicated to prevent a halt of an entire system.
Therefore, a fault-tolerant system capable of selectively replicating predetermined functions requiring continuity or stability is necessary.